Singlet oxygen (SO), an electronically excited oxygen molecule, is believed to be a major intermediate in a variety of physiologic, pathophysiologic and therapeutic processes including the neutrophil respiratory burst, the oxidative metabolism of microsomes, the actions of a number of antineoplastic drugs (daunorubicin, doxyrubicin, mitomycin C , procarbazine and bleomycin) and paraquat poisoning. Past chemiluminescent (CL) and wet chemical studies have been unable to determine the role of SO in these processes. A new CL spectrometer has been developed with the ability to automatically produce spectra from ultra-weak CL sources and with a sensitivity to the 1268 nm band of SO, 2,000 times that of previously described CL spectrometers. Preliminary results demonstrate that 1268 nm CL can detect SO at concentrations less than 1% of that detectable with the dimole CL (the conventional technique). The 1268 nm band appears free of interference from other CL sources. The measurement of both visible and 1268 nm Cl permits a clear distinction between SO CL and CL from other sources. CL studies of all the systems listed above are planned to clarify their underlying mechanisms. A number of chemical and enzymatic models of these processes will also be studied. Several clinical studies will be undertaken in patients with malignant neoplasms. This is a completely unexplored area. Patients with myeloproliferative diseases will be studied. Correlations between neutrophil CL, the type of disease (e.g., polycythemia vera), the current therapy and the course of the disease will be made.